Wind turbine power systems, such as doubly-fed induction generator (DFIG) wind turbine systems, often include a power converter. For example, DFIG wind turbine systems can include a power converter with an AC-DC-AC topology, wherein a rotor side converter converts AC power from the rotor to DC power at a DC bus, and a line side converter converts the DC power from the DC bus to AC power suitable for an electrical grid. Thus, power generated by the DFIG can be provided to an electrical grid via two paths. For example, the stator of a DFIG can be synchronously connected to the electrical grid, while power generated by the rotor of the DFIG can be provided to the grid via the power converter.
The DFIG can be configured to provide both real power (measured in Watts) and reactive power (measured in VARs). For example, by controlling the switching cycle of the rotor side converter, the real and reactive power generated by the stator can be controlled. Similarly, by controlling a switching cycle of the line side converter, the real and reactive power generated by the rotor can be controlled. Thus, the combined amount of reactive power generated by the DFIG wind turbine system can be controlled to meet a reactive power production requirement, such as a reactive power production requirement set by a dispatch control system of a utility company.
In a typical configuration, the stator of a DFIG can be configured to supply the reactive power for the system unless the stator runs out of current margin, in which case, the line side converter can be used to help make reactive power to meet the reactive power production requirement. However, in such a configuration, the stator may be subjected to increased stresses as compared to the line side converter. For example, the stator may be subjected to increased currents, temperatures, losses, or other stresses that can reduce the efficiency and operating life of the DFIG. These increased stresses can cause the DFIG to wear out at a faster rate, increasing replacement costs and decreasing system availability and reliability.